This invention relates generally to optical imaging systems located on a platform, for example an aircraft, and more particularly to a stabilized optical gimbal assembly used in connection with a forward looking infrared target acquisition and tracking apparatus utilized in weapons delivery systems.
Sophisticated optical imaging systems normally require some sort of sealed enclosure, particularly when exposed to the elements. When the optical imaging system is mounted on an aircraft, particularly high performance military aircraft, it is extremely important to keep the size of the sealed enclosure as small as possible in order to minimize the aerodynamic effects on the aircraft. The enclosure inherently includes some type of window through which the internal optical system can view the outside world. In order to increase system efficiency, it is necessary to make this window as large as possible in order to maximize the amount of light that can be collected for imaging and is referred to as the "clear aperture" and is one of the most important parameters in determining system performance. Accordingly, one of the major problems in any system design is to maximize the clear aperture size in the smallest possible enclosure. In other words, one attempts to maximize the ratio of clear aperture diameter to enclosure diameter or some other maximum dimension.
The optics, moreover, are normally mounted on a stabilized gimbal located just inside the window. The gimbal directs the line of sight of the optical system in azimuth and/or elevation relative to aircraft coordinates, thereby generating what is referred to as the "field of regard" of the system. The larger the field of regard, the better. Where the system is used to track targets for a weapons system, the gimbal must also be well stabilized so that any jitter in the image displayed to the operator is eliminated. All of this requires motors, resolvers, gyros, bearings, well known to those skilled in the art which complicate the problem of maximizing the ratio of clear aperture to enclosure diameter.
Gimbal enclosures are typically referred to as shrouds or turrets. As a result, one attempts to maximize the ratio of the clear aperture diameter as measured at the outside surface of the windows to the turret outside diameter. Many different optical gimbal schemes have been previously designed in an effort to maximize the ratio of clear aperture diameter to turret outside diameter but have been known to achieve a ratio only on the order of 0.50.